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The above aminodiester was alternatively prepared in the following manner. Diethyl 2-aminononanedioate (10.40 g) and oct-1-en-3-one (5.04 g) were mixed slowly at 0° C. with stirring, and set aside at room temperature for 3 hours, giving diethyl 2-(3-oxooctylamino)nonanedioate as a colourless oil, δ2.3(4H, multiplet, -CH2 -CO2Et and NCH2CH2CO-), 3.16(1H, triplet, EtO2C-CHR-N), 4.11(2H, quartet, --O--CH2 --CH3), 4.17(2H, quartet, -O-CH2 -CH3). A stirred solution of this ketone (13.5 g) in absolute ethanol (140 ml) was treated dropwise at 0° C. with sodium borohydride (665 mg) in absolute ethanol (70 ml), then kept for 31/2 hours at room temperature and concentrated at 40° C. in vacuo. The residue, dissolved in water, was brought to pH 5 with N-hydrochloric acid and extracted thoroughly with chloroform, the extract was washed with water, dried, and evaporated, giving diethyl 2-(3-hydroxy-octylamino)nonanedioate as a colourless oil. Without further purification, the latter was dissolved in dihydropyran (14.0 ml), treated with ether (10 ml) followed by p-toluenesulphonic acid (6.72 g) in portions, and set aside at room temperature for 18 hours. The reaction solution was diluted with ether, washed with aqueous sodium carbonate then water, dried, and evaporated, and the residue was purified by column chromatography on silica in 1:4 hexane/ether, giving diethyl 2-(3-(tetrahydropyran-2-yloxy)octylamino)nonanedioate identical (n.m.r., i.r. mixed t.l.c.) with that prepared previously.